Television apparatus



March 21, 1939. w. .1. PocH TELEVISION APPARATUS Filed May 5l, 1955 2 Sheets-Sheet l RWD/0 FECEI VER .Qu N

CIRCl//f March 2l, 1939. v W, J, POCH 2,151,149

TELEVISION APPARATUS Filed May 5l, 1935 2 Sheets-Sheet 2 F5 f-f VERT/CHL OUTPUT Patented Mu. 21,1939

TELEVISION APPARATUS Waldenm- J. linen, columna. N. J., mim

to Radio Corporation of America, a corporation o! Delaware Application May 8l, 1935, Serial No. 24,206

BClaims.

My invention relates to television apparatus and particularly to means for separating synchronizing signals from picture signals at a television receiver. y

In British Patent No. 407,409 there is described a television system in which scanning at the receiver is maintained in synchronism with scanning at the transmitter by transmitting a horizontal synchronizing impulse of short duration 10 at the end of each scanning line and a vertical synchronizing impulse .of the same amplitude and longer duration at the end of each picture frame. The synchronizing impulses are of greater amplitude than the picture signals and preferably are in the black direction.

An object of my invention is to provide an improved method of and means for separating synchronizing impulses from picture signals in a system of the above-described type.

A further object of my invention is to provide an improved picture signal and synchronizing impulse separating circuit for television receivers which does not reverse the polarity of the synchronizing impulses.

Vg5 In a preferred embodiment of my invention I impress the combinedpicture and synchronizing signals upon a vacuum tube of the diode type, the synchronizing signals having a positive polarity when impressed upon the diode and having the same polarity when they appear in its output circuit. In order to prevent any positive polarity picture signals which may be present from appearing in the diode output circuit, a negative bias is applied to the anode of the diode,

this bias having a value such that only the positive synchronizing impulses have an amplitude great enough to make the anode positive and thereby produce a ow of current through the diode.

Preferably a biasing means is provided which biases the anode negatively .by an amount which van'es in accordance with the amplitude of the incoming signals.

Other objects, features and advantages of my invention will appear from the following description taken in connection with the accompanying drawings in which lFigure 1 is a circuit diagram of a television receiver embodying my invention,

Figs. Zand 3 are curves which are referred to in explaining the operation of the circuit shown in Fig. 1,

Fig. 4 is a circuit diagram of another embodiment of my invention, and

Figs. 5 to 9 are curves which are referred to in (Cl. P18-7.5)

explaining the operation of the circuit shown in Fig. 4.

Referring to Fig. 1, there is illustrated a television receiver which is designed to receive picture and synchronizing impulses which have been transmitted by means of a modulated carrier wave in accordance with the teachings of the above-mentioned British patent. The receiving apparatus includes a radio receiver i which selects and demodulates the desired carrier wave 1o whereby picture signals and synchronizing impulses of the character described above appear in the output circuit thereof.

The picture signals and synchronizing impulses are amplified in resistance coupled amplifiers 15 2 and 3 and impressed upon the control grid 4 of a cathode ray tube 6. The cathode ray tube 6 may be of well known construction comprising an evacuated envelope having therein a cathode 1, the control grid 4, a ilrst anode 8, and a sec- Qq ond anode 9. Suitable deiiecting means, such as deecting coils Il and i2', are provided for deiecting the cathode ray both horizontally and vertically to eiect scanning of a uorescent screen i3 at the end of the tube. 2.-

'I'he horizontal deiiecting coils l2 are supplied with saw-tooth current having a comparatively high frequency from a horizontal deiiecting circuit indicated at i4. The vertical deilecting coils Il are supplied with saw-tooth current having 30 a comparatively low frequency from a vertical deiiecting circuit indicated at I6. The deecting circuits may be any of several well known designs, such circuits generally including a relaxation or blocking oscillator which can be locked 3- in step with synchronizing impulses impressed thereon.

The number of amplifier stages in the radio receiver l is so selected that the polarity of the synchronizing impulses impressed upon the control grid 4 of the cathode ray tube is negative whereby the cathode ray is blocked at the end of each scanning line, this being desirable in order to prevent a trace on the fluorescent screen during the return line period.

The scanning of the uorescent screen i3 by the cathode ray is maintained in synchronism with the scanning at the transmitter byb separating the synchronizing impulses from the picture signal and impressing these impulses upon the 50 deflecting circuits i4 and I6. In accprdance with my' invention the combined picture signals and synchronizing impulses are taken from a point in the circuit, such as the output circuit of the amplier 2, where the synchronizing impulses are u of positive polarity and areimprmed upon a ,L separating circuit I 1.

The separating circuit I 1 comprises a vacuum tube I8 of the diode type having an indirectly heated cathode i9 and an anode 2l. 'Ihe cathode I! is connected to ground through an output resistor Rz while the anode 2l is connected to grormd through an input resistor Rr which, preferably, has a large resistance value compared with that oi.' Rz. Thus the circuit between the cathode I9 and the anode 2l. includes two resistor sectionsor elementsconnected'in series.

The'picture signals and the synchronizing impulses are fed to the anode 2| through a ,condenser 22 whereby they are impressed across the input resistor R1.

For reasons which will be explained hereinafter, only the synchronizing impulses appear in the output circuit of the separating tube I8, these impulses being fed through a. conductor 23 to` two lter circuits 24 and 26. The lter circuit 24 includes a resistor 21 of fairly high resistance value connected in seri with a condenser 28 having comparatively large capacity whereby only the lower frequency vertical synchronizing impulses appear acrossthe condenser 28. Preferably; the vertical synchronizing impulses are supplied through a potentiometer 29 in shunt to the condenser 28 to the vertical deilecting cir-v' cuit I6.

The lter circuit 26 consists of a small capacity condenser 3i connected in series with a. resistor 32 of fairly low resistance value whereby only the comparatively high frequency horizontal synchronizing impulses pass through the condenser 3l to develop voltage impulses across the resistor 32 which are impressed upon the hori-` zontal deecting circuit I4.

Referring now to the operation of the picture separating tube I8, the positive synchronizing impulses impressed upon the anode 2i cause a :dow ofscurrent through the diode whereby the condenseri22 receives a charge. The charging circuit `may be traced from the upper end of the plate resistor 33 oi.' the ampliiier 2, through the conductor 36, the condenser 22 and diode I8, and

through the output resistor Rz and ground to the cathodeof the amplier 2. Between successive horizontal synchronizing impulses, a portion of the charge on the condenser 22 leaks oil' through the input resistor but the time constant of the circuit including the condenser 22 and the input resistor R1 is such that a substantially steady negative bias is applied to the anode 2| so long as there is no charge in the amplitude of the incoming synchronizing impulses.

The action of the circuit will rbe better understood by referring to Figs. 2 and 3. The curve in Fig. 2 represents a composite signal consisting of picture signals 28 and horizontal synchronizing impulses 25 appearing in the output circuit of the ampliiier 2. It will be noted that the greater part of the picture signals have a nega-- tive polarity with respect to the alternating current axis and that the synchronizing impulses have a positive polarity. It will also be noted that the amplitude of the synchronizing impulses is greater than the amplitude of any positive K polarity picture signal.

It will be apparent that there can be no current iiow through the diode I8 until the amplitude of a positive polarity impulse impressed upon the anode 2I is sulcient to overcome lthe negativey bias. Therefore, if the bias is of the magnitude indicated in Fig. 2only the peaks oir the synchronizing impulses will appear in the output re-` sistor Rz as shown inFlg. 3. If the amplitude of the incoming signals increases, the negative bias increases correspondingly with the result that, even though the amplitude of the picture signals has increased; their amplitude is still insufcient to overcome the bias and only the synchronizing impulses appear across the output resistor Rz.

Instead of iirst separating the synchronizing signals from the picture signals and then separating the horizontal synchronizing impulses from the vertical synchronizing impulses as described above, the illtering of the horizontal and vertical synchronizing impulses may be done before the picture signals are removed. This method of separation has certain advantages as of thevcircuitshown in Fig. 4. In practicing the invention illustrated in Fig. 4, the composite signaltwhich appears in the output circuit of the amplier 2 is impressed through a coupling condenser 31 upon two filter circuits 38 and 39. The lter circuit 38 may consist of a small capacity condenser 4I and a comparatively low impedance resistor 42 connected in series, this illter being similar to the lter 26 shown in Fig. l. The filter 39 may consist of a resistor 43 connected in series with a condenser 44 of comparatively large capacity.

The signals which are impressed upon tle illters 38 and 39 are `represented by the curve in Fig. 5 where the picture signals are represented at 46 and the horizontal and vertical synchronizing impulses are represented at 41 and 48, respectively. The signal appearing across the lter resistor 42 is represented in Fig. 6. It will be seen that the amplitude of the vertical synchronizing impulse 48 has been considerably reduced with respect to the amplitude of the horizontal synchronizing impulses 41. The signal appearing across the lter resistor 42 is impressed upon a thermionic diode 49 through a condenser 5I. The diode circuit is the same as the one previously described and includes an output resistor 52'connected between the cathode 53 oi.' the diode 49 and ground and an input resistor 54 connected between the anode 66 of the diode 49 and ground.

The flow of diode current produced by the horizontal synchronizing impulses causes a negative bias to be appliedfto the anode 56 as indicated in Fig. 6 whereby only the peaks of the horizontal synchronizing impulses appear across the output resistor 52. It will be understood that the negative bias is given a valuer such that the amplitude of the vertical synchronizing impulse 48 is insuillcient to overcome the bias. Therefore, the output of the diode includes only horizontal synchronizing impulses as represented by the curve in Fig. 7.

The signal which appears across the condenser 44 of thekvertical iilter circuit 39 is represented by the curve in Fig. 8. It will be seen that in this circuit the horizontal synchronizing impulses 41 have been so attenuated that their amplitude is considerably less than the amplitude of the vertical `synchronizing impulse 48. This signal is impressed upon a. second diode 51 through a condenser 58 whereby the anode 53 of the diode 51 is biased negatively by means of thetheinmtresistorisgreatencushtcpremenu-geanthelfromleak- Aof 80 cycles per second.

Prom the foregoing description `it will be apparent that various modifications may be made in my invention without departing from the scope.

and spirit thereof and I desire, therefore, that only such limitations shall be imposed thereon as are necessitated by the prior art and set forth in the appended claims.

I claim asV my invention: .1. In a television receiver o1' the type which includes a cathode ray tube having deilecting devices for deilecting the cathode ray and of the type having deecting circuits coupled to said deilecting devices, an electric discharge tube having a cathode vand an anode, two resistor elements connected in series between said cathode and said anode. a condenser, means for impressing received picture and synchronizing signals across one of said resistor elements through said condenser with the synchronizing signals in a di rection to produce current iiow through said discharge tube and means for coupling the other of said resistor elements to at least one of said deilecting circuits, the time constant of the circuit including said resistor being such that said anode is maintained negative with respect to said cathode between successive synchronizing 2. In a television receiver for separating positive polarity synchronizing impulses from picture signals of less amplitude in the positive direction with respect tc an alternating current axis than said impulses, an electric discharge tube having a cathode and an anode, a utilization circuit for said impulses, two resistor sections connected in series between said anode and said cathode, said utilization circuit being coupled across the said resistor section adjacent to said cathode, a condenser, and means for impressing said positive impulses across a portion of said resitive circuit adjacent to said anode through said condenser whereby it receives a charge periodically, the time constant of the circuit including said condenser and said last resistor section being such that a substantiallysteady voltage appears across said last portion whereby said anode is maintained negative with respect to said cathode by an amount greater than the amplitude ofsaid picture signals in said positive direction.

3. A separating circuit in a television system of the type in which picture signals and .synchronizing signals are transmitted and in`which at least the greater part of the picture signal voltage is of opposite polarity to the synchronizing signal voltage with respect to a given ci! any substantial amount between vertical axis, and ci' the type in which the receiver includes a kcathode-ray having a horizontal deiiecting device and a'vertical deilecting device,

a saw-tooth wave generator coupled to said first device, a saw-tooth wave generator coupled to said second device. said separating circuit comprising an electric discharge tube having a cathode and an anode, two resistor sections connected in series between said cathode and said anode, means for coupling said generators across one of said resistor sections, a condenser, means for vimpressing said picture signals and said synchronizing signals across the other of said resistor sections through said condenser with said synchronizing signals having a polarity such that they cause current ilow through said discharge tube, the time constant of the circuit including said condenser and said other resistor section having a'time constant such that said anode is maintained negative between synchronizing signals.

4. A separating circuit in a television system of the type in which a carrier wave is modulated by picture signals and by both horizontal and vertical synchronizing impulses, and in which said impulse modulation is introduced into the carrier in the same direction as the modulation thereof by dark portions of a view being transmitted. and of the type in which the receiver includes a cathode-ray tube having deflecting devices and two saw-tooth wave generators coupled thereto, said separating circuit comprising a vacuum'tube having a cathode and an anode, two resistor elements connected in series between said cathode and said anode, means for impressing said signals and impulses upon one of said resistor elements through a condenser with the 'synchronizing impulses having a polarity such that they cause current ilow through said vacuum tube, the time constant of the circuit including said Vcondenser being such that said anode is maintained negative between synchronizing impulses, and means for impressing the synchronizing impulses appearing across the other of said resistor elements upon said generators.

5. In a television receiver adapted to receive a carrier wave modulated by picture signals and by both vertical and horizontal synchronizing impulses, said impulses all having substantially the same amplitude, said amplitude being greater than the peak amplitude of picture signals of the same polarity as said impulses, the method of .operation which comprises in one channel decreasing the amplitude of one of said groups of synchronizing impulses with respect to the other group of synchronizing impulses, next separating out said other group of synchronizing impulses substantially to the exclusion of said picture signals, and then utilizing said other group of synchronizing impulses for synchronizing, and further comprising in a second channel separating out said one group of synchronizing impulses substantially to the exclusion of said picture signals, and then utilizing said one group of synchronizing impulses for synchronizing.

6. In a television receiver adapted to receive a carrier wave modulated by picture signals and by both vertical and horizontal synchronizing impulses, said impulses all having substantially the same amplitude, said amplitude being greater than the peak amplitude of picture signals of the same polarity as said impulses, the method which comprises in one channel decreasing the 4 I i zum amplitude o! nid vertical impulses with yrespect to seid horizontal impulses. next separating out t said horizontal impulses to the exclusion o! saidk picture signals. and then utilizing saidfhorizontai impulses for synchronizing.

WALDEMIAR J. POCH. 

